1. Field of the Invention
The present invention generally relates to an image processing apparatus, and particularly relates to a moving-picture processing apparatus provided with a pre-fetch memory for pre-fetching and storing a portion of a reference picture stored in an external memory.
2. Description of the Related Art
In a decoder or encoder using a moving-picture compression method such as MPEG (Moving Picture Experts Group), there is a need to store a reference picture in an external memory and to retrieve a rectangular portion of the reference picture stored in the external memory during a decoding process or encoding process. Depending on types of processes, multiple read accesses may need to be performed with respect to the same portion of the reference picture stored in the external memory. This is one of the causes that increase the amount of data transfer between the external memory and the decoder/encoder.
In order to avoid multiple read accesses with respect to the same portion of a reference picture stored in the external memory, a pre-fetch memory may be provided in a decoder or encoder to store a portion of the reference picture stored in the external memory in such a manner that the pre-fetched portion is updatable. With this configuration, the decoder or encoder can retrieve a necessary portion of the reference picture from the pre-fetch memory. This makes it possible to reduce the amount of data transfer between the external memory and the decoder/encoder.
[Patent Document 1] Japanese Patent Application Publication No. 2005-102144
[Patent Document 2] Japanese Patent Application Publication No. 2006-31480